In a Clash of Kings,
As Daenerys visits the docks of Qarth in order to find passage, Ser Jorah alarms her that they are being followed by two men, a fat brown man (15 stone weight and covered in scars) and an older man with a Westerosi appearance (with a white beard and a staff). Ser Jorah and Daenerys notice the men using a large brass platter in a ship and attempt to escape them. Just then the brass merchant takes after them and pesters them to buy the platter which they do just to get rid of the man.
At that moment, the Qartheen thrusts a carved wooden case disguising it to be a gift to the Mother of Dragons which on opening seems to contain a valuable scarab. As she reaches for it, the scarab unfolds with a hiss. But before the manticore could sting her, whitebeard sends the box pummeling away with his staff and crushes the creature with the end of his staff. Danys' bloodriders attempt to confront the two men but she narrates the incident to them and by the time she sends out her bloodriders to nab the perpetrator, A Sorrowful Man, he has since long disappeared.
The two men turn out to be Strong Belwas and Whitebeard.
In A Clash of Kings, Daenerys turns to the Warlocks after she's refused aid by the Pureborn, the ruling elite of Qarth. Daenerys' dragons kill the Undying Ones to save their "mother" from the ancient warlocks. After Daenerys leaves the House of the Undying, many Qartheen factions, including the warlocks, call for Daenerys to be killed and one of them sends a Sorrowful Man to assassinate her. Pyat Pree also gathers the remaining warlocks to work ill on Dany.
The TV series changed the Sorrowful Man assassin hired by one of the Qartheen factions to a warlock who appeared as a young girl, though both attempted to kill her with a poisonous Manticore. Also, in the books the assassination attempt occurred as Daenerys was leaving the docks of Qarth, while the TV series slightly changed this by having it occur at Astapor's docks just as she arrived from Qarth.